Stencil making



Aug. 23, 1960 MQTT 2,949,848

STENCIL MAKING Filed July 2?, 1955 IN VEN TOR.

BYF Q A Wang GEORGE R. MOTT United States Patent" STENCIL MAIGNG GeorgeR. Mott, Rochester, N.Y., assignor to Haloid Xerox Inc., a corporationof New York Filed July 27, 1955, Ser. No. 524,657

7 Claims. c1.'101-12s.3

This invention relates in general to master making for duplicatingprocesses.

The present method for producing stencils for stencil duplicatingprocesses involves the cutting of a wax 1mpregnated porous tissue paper.The cut stencil permits passage of an aqueous ink directly from areservoir of ink to the final copy through the openings. Analogousprocesses have been evolved for the graphic arts wherem a silk screen isblocked by a manually applied binder or by photographically controlledgelatin layers. The screen is then used to control the flow of ink orpaint from an applicator to the paper or other final support.

This invention presents a method whereby duplicating stencilsmay beprepared xerographically. In particular, a special binderphotoconductive plate is used to produce a stencil by serving both asthe image forming and stencil forming medium. This provides for the useof existing documents as original copy and thereby eliminates thedisadvantages of manual preparation as, for example, typing, drawing orthe like of stencils. Although photochemical stencils exist, theygenerally must be prepared using a high contrast photographic positiveto which the stencil is exposed while clamped in close contact. Thisinvention also overcomes the problem of contact exposure, as well as theneed for high contrast photographic positives.

It is an object of this invention to devise new means and methods offorming a master.

It is a further object of this invention to devise new means and methodsof forming stencils, silk screen masters or the like through the use ofxerography.

It. is a still further object of this invention to devise new means-andmethods of forming stencils, silk screen masters or the like while usinga special binder photoconductive plate.

Additional objects of the invention will in part be obvious and will inpart become apparent from the following specification and drawings, inwhich:

Fig. 1 is a fragmentary cross-sectional view of a binder intended to beused in this in- Fig. 8 illustrates stripping of the cover sheet andremoving the image and portions of the binder photoconductor from theplate.

Fig. 9 illustrates softening of the remaining binder material.

Fig. 10 shows attaching of a transfer sheet to the softened bindermaterial.

'Fig. '11 shows removal of the transfer sheet and re- Patented Aug 2 3,1960 maining binder material, resulting in a master for subsequent use.I

Referring now to the drawings, in Fig. 1 is shown a cutawaycross-section view of a special plate to be used inv forming mastersaccording to this invention. The plate, generallydesignated 13, iscomposed of a photo-' conductive insulating material 11 overlying a baseor support layer 12. Various photoconductive insulating materials may beused. One, which is fully described in the Middleton and Reynoldsabandoned co-pending. application Serial No. 311,546, filed September25, 1959. and which comprises zinc oxide in a resininsulating bind-- er,is presently preferred. Suitable resin bindersinclude silicone resinssuch as DC-996 (Dow Coming) and SR -82 v (General Electric). Variousother photoconductive insulating layers comprising photoconductivematerials in in sulating-binclers which may be used as thephotoconductive insulating layer of the plate used in this invention arealso disclosed in that co-pending application. Such other, materialsinclude, but are in no way limited to, zinc-- magnesium oxide, zincsulfide, zinc cadmiumsulfide,

cadmium sulfide, cadmium strontium sulfide, zinc silicate;. calcium'tungstate, selenides and mixed selenides, of cad,-,

mium and zinc, anthracene, titanium dioxide, and the Desirably, thesematerials are activated with small like.

amounts, that is 0.01% to 0.001%, of metallic impurities, as iswell-known to those skilled in the art.

The base material 12 is preferably a conductive material such as thevarious conductive metals, conductive glass, conductive flexiblematerials such as conductive. foils, flexible materials spattered withconductive metals,

or the like. Two materials which have been found particularly valuableas the base layer 12 are conductive foil and paper which is impregnatedwith a, conductive.

material or which, when used, is made conductive by moistening withwater or the like.

Reference is now had to Fig. 2 wherein the charging or sensitizing stepis illustrated. As shown in this figure,

the grid 16 whereby a corona discharge isproduced around the wires.

Acontrol grid 18 of coarser wires is.

located between corona grid 16 and layer 11 on support 1 plate 12, thesecond grid 18 being held at an intermediate potential of severalhundred volts above ground potential.

Grid 18 serves to control or limit the potential placed upon layer 11and prevents overcharging. The'potentials are supplied by a high voltagepower supply circuit 20, such as a transformer rectifier circuit and avoltage dividing resistance for supplying the required potentials togrlds 18 and 16. Since charging makes the plate 13 sensitive to light,charging is carried out in darkness' Desirably also, the support base 12which is conductive ductive insulating binder layer 11 is sensitive tolight or during charging is grounded. After charging, photoconotheractivating radiation and is exposed, as for example as is illustrated inFig. 3.

In Fig. 3 there is shown copy to be reproduced gening binder layer whichoverlies backing support i erally designated 21, a lens designated 29.,and a plate 13 Material to be copied from plate 13... During exposure,the, electrostatic charge which.

has been applied to the surface of layer :11 is dissipated in the areaswhich are struck by light to leave a charge pattern remaining wherelight did not strike the surface of plate 13, as in black lines andletters of the image.

The electrostatic charge pattern formed on layer lfis the image whichwill subsequently be developed bybringingfinely divided material such asfine powders into contaet with the surface of layer 1 1. Althoughprojection of an optical image is illustrated in this figure, it is tobe realized that other techniques of image formation known to the artare intended to be included herein. For example, the charge pattern onthe surface of layer 11 may be formed by exposing a charged plate to, anX;ray pattern or other radiation patterns or by depositing charges on anuncharged plate in the form of a pattern or image, or the like. Suchimages produced by any of these various methods may be continuous tonepatterns in which the charge varies gradually in density from point topoint, or may be images with large black, gray and white areas as wellas images of lines and characters.

In Fig. 4 there is illustratedone technique of develop ment of theelectrostatic charge pattern. The technique of development illustratedin this figure has become known as loop development in that the plate isformed into a loop and the loop carries the developer powder, which iscascaded across the surface of the photoconductive insulating binderlayer 11 of plate 13 as the loop is varied. Loop development may becarried out when using a flexible plate, in that the weight of thedeveloper material 23 is utilized to cause the loop to change itsposition as the hands are moved upward and downward. In this figurethere is illustrated the fingers of two hands gripping the edges of theplate 13 and preferably gripping only extended portions of the basematerial 12 to thereby avoid distorting the charge pattern formed on thesurface of the photoconductive insulating binder material.

' It is to be realized, of course, that the technique illustrated may beadapted to mechanical operation and that although loop development isillustrated in this figure, there is no intention to exclude othertechniques of development known to the art. The intention is instead, toinclude all known techniques of development. Such other techniquesinclude, but are in no way limited to, cascade development described inWalkup 2,618,551 and powder cloud development, which is development bybringing a cloud of powder particles in gas to the surface carrying theelectrostatic charge pattern for deposition of particles in areas ofcharge. One technique of development which has been found valuable fordevelopment of ima-ges formed on a plate in which the binder layer is alayer of zinc oxide in an insulating resin binder is what is generallyknown in the art as magnetic development. In magnetic development amagnet is used to attract and hold particles which are electrostaticallyattracted to the charge pattern on the charge pattern bearing surface.These particles form, in efiect, a brush on the magnet and are brushedacross the surface carrying the charge pattern and deposit in imageconfiguration. Magnetic development, cascade development, and powdercloud development may be used for rigid as well as flexible plates.Other techniques of development generally known to thosein the art arealso intended to be included herein.

In Fig. is illustrated tackification of a toner image. Theplate 13comprising support layer 12 and insulating binder layer 11 supportstoner image 25 on the surface of insulating binder layer 11. The plate13 is placed in an area filled with vapors which act as a solvent forthe toner material. In this figure, the vapors 26 are shown surroundingand encompassing toner image 25.

Tackifioation of the toner image is accomplished when the powder imagebecomes a more liquefied adhesive unit. Although it is not desired tolimit this invention to a particular mode of operation, it is nowthought that tackification takes place. due to the effect of vapors onthe viseosities and surface tensions of the materials making upthe'image. It is believed that exposing the image to 4 proper vapors causesthe surface tensions of the materials to decrease, thereby makingparticles more adhesive. This will cause the particles to stick to oneanother and at the same time cause the image itself to become adhesive.It is thought in general that solvents for image materials or, moreparticularly, vapors soluble in the image materials cause a lowering ofsurface tensions. Exposure to vapors also causes the viscosity of thematerials making up the image to fall, thereby allowing the particles toflow more readily. Exposure to vapors causes the image to reach thistacky state by decreasing the viscosities and surface tensions of thematerials comprising the image, thereby producing a more liquefiedadhesive single image body. The image should be composed of materialswhich can be reacted on as indicated by proper vapors.

Although tackification has been described in terms of vaportackification, it is also to be realized that heat tackification and thelike are intended to be included herein. For example, applying heat tothe toner image will also react on the viscosities and surface tensionsof the materials making up the image. Thus, applying the proper amountof heat will cause tackification of the image when the image materialsare such that they will be reacted on by heat. Heat tackification byradiation and conduction are intended to be included herein;

Reference is now had to Fig. 6 wherein is shown the placing of a sheetagainst the tacky image. The tacky image 25 formed in Fig. 5 on layer 11backed by support 12 of plate 13 is covered in this figure with thecover or transfer sheet 27. This sheet may be paper, plastic, or othermaterial to which the tacky toner image will adhere. If the transfersheet 27 is porous to the vapors used to tackify the image, which islikely the case, the sheet 27 may be placed in contact with thedeveloped image be: fore and during the tackification step and thesandwich comprising the plate, the developed image and the cover sheetmay be fed directly from tackificati'on to the pressing step illustratedin Fig. 7. When using heat for tackification as described in connectionwith Fig. 5, the assembled layers or sandwich may also be subjected toheat with the cover sheet in place.

In Fig. 7 is shown pressing of the cover sheet against the surfacecarrying the tacky image. In this figure pressure is applied by movingthe sandwich made up of plate 13, toner image 25, and cover sheet 27,between rollers 28. As indicated, the toner image resides on insulatinglayer 11 backed by support layer 12. Although pressure is applied inthis figure using rollers, it is to be realized that other pressureapplying techniques generally known to those in the art are intended tobe included herein. For example, pressure may be applied by positioningthe sandwich between two flat surfaces and pressing the surfacestogether, or pressure may be applied by placing the sandwich on a solidbase and rolling a roller across the surface, or the like.

In the instance when heat is applied to tackify the image, it has beenfound that the steps described in connection with Figs. 5 and 6 may becombined with the pressure step of Fig. 7. Thus, it is possible to usetwo heated platens which may be pressed together. In such an instancethe sandwich is placed on one platen and the other platen is placedabove the sandwich and pressure is. applied and the combination heatand, pressure step will prepare the toner image and binder layer for thenext step in this process.

v Preferably, after the cover sheet 27 is pressed against the tackyimage 25, the image is allowed to dry or cool to allow the image to fuseagainst the surfaces it is in contact with and the cover sheet is thenstripped away aseasae fnaterial 30. The binder material covers all areasof the toner image and thus creates a plate 13 void of binder materialin image areas. The remaining binder layer on plate 13, after thestripping operation, is to serve as the blocking agent for the poroussupport of the end product of this invention, a cut master forduplicating processes.

In Fig. 9 is shown the next step of the master making processof thisinvention. In this figure support layer 12 carries on its surface thebinder layer lacking areas transferred to the tacky image described inconnection with Fig. 8. This binder layer is now softened or made tackyby exposing it to vapors which are soluble in the binder material or bythe application of heat or the like This tackification step is carriedout as was tackification of the developed image, the time of exposure toheat or vapors depending on the time needed to soften the bindermaterial.

While the binder layer is in the softened or tacky state, a sheet ofporous material is placed in contact with the upper surface of binderlayer 11. This step is illustrated in Fig. 10 wherein a sheet of porousmaterial 31 is placed in contact with layer 11 which is supported bysupport base 12. This sheet is to act as the base or support sheet ofthe master. Thus, when the master is to be used for stencil duplicating,sufficiently strong tissue paper or the like may be used. When themaster is to be used for silk screen printing, a proper silk screen baseis used. The sheet 31 is attached to layer 11 through the use ofpressure as described above in connection with Fig. 7. That is, thesandwich may be moved between rollers, may be pressed between surfaces,may be placed on a support surface and pressure applied using a rolleror the like, or the surfaces may be pressed together through the use ofelectrostatic tacking by spraying corona discharge to sheet 31 whilebase 12 is grounded or is in position on a grounded conductor. Othertechniques of applying pressure to attach the support sheet 31 to layer11 will occur to those skilled in the art and are intended to beincluded herein.

Fig. 11 shows the removal of layer 11 from support base 12 to sheet 31.The pressing of sheet 31 against layer 11, as described in connectionwith Fig. 10, results in intimate contact between the softened bindersurface and the binder sheet. As the binder layer 11 hardens, fibersfrom sheet 31 become imbedded in the binder layer and a permanent bondbetween the two is formed. Sheet 31 should also be chosen because ofbasic characteristics in the sheet material which create greateradhesion between the binder layer 11 and the surface of sheet 31 ascompared to the adhesion between binder layer 11 and the surface ofsupport base 12. Most tissue papers have this bonding or adhesivecharacteristic which is desired and also have the porosity and strengthrequired for a stencil base sheet to be used on stencil duplicatingmachines.

The stripping step may also be accomplished by softening onlyselectively the top and bottom of the binder layer 11 without greatlyaffecting the central area. This may be accomplished by exposing thebinder material to vapors while wetting base material 12 with a liquidsolvent for the binder material.

It is also possible to construct the binder plate with three layersrather than two as previously discussed. The additional layer may be anintermediate between the binder layer and the support base. Such a layermay be used to facilitate the complete release of the binder layer fromthe paper base during the step described in connection with Fig. 11. Forexample, such an intermediate layer may be composed of a water solublematerial. The exposure of the binder material to heat or vapors solublein the binder material will soften the top surface to such an extent toallow a bonding between the upper surface and the new base sheet.Wetting the support base of the plate at the same time or a subsequenttime will release the binder material to-the new base, thereby creatinga" cut master to be used for duplicating processes.

The master formed according to the techniques of this invention may thenbe attached to a stencil machine for a normal stencil run. The ink insuch an instance is fed through the stencil pad and then through theporous areas of the tissue.' The areas to which the binder material wastransferred will block passage of ink and thus there will be printed onthe copy sheet pressed against the master an inked image correspondingto the original. In the instance when the master is used for silk screenprocesses, ink is applied through the porous areas allow: ingapplication to the copy sheet and thus reproduction of the image cut inthe master.

Various xerographic developer materials have been Such materials foundto work well in this invention. are available under the trade mark Xeroxand are sold as Developer or Toner by The Haloid Company of Rochester,New York. Also, the compositions of proper developer materials aredescribed in Walkup US. Patent 2,618,551 and Walkup and Wise US. Patent,638,416. As shown in the Walkup patent, a suitable developer comprisesa 20 to 1 mixture of Amberol F-71 phenol-formaldehyde resin (Rohm & HaasCompany, Philadelphia) and carbon black. The mixture is ball milled,melted together, cooled, and ground into fine particles. Otherdevelopers and toners generally known to the art have also been found towork well with this invention.

When vapor tackification is being used, the particular removed to thecover sheet, the same solvent vapors may.

be applied to the binder material for a longer period for a morethorough softening so the binder material itself may be transferred.Similarly, when heat is being used, proper timing in the first instanceto tackify completely image areas and to affect only slightly the bindermaterial itself should be used, causing selective transfer of imageareas of the binder with transfer of the developed image. When heat isapplied to transfer the binder layer after transfer of the bindermaterial beneath image areas,

longer exposure to heat or higher temperatures are de-' sirable to bringabout complete tackification. However, it is desirable to bring aboutcomplete tackification without a flowing of the binder material intoareas of binder removed from the developed image to thereby reproduceclean copy when the master is used for its intended purposes. Varioussolvent vapors may be used, as for example, trichloroethylene,chloroform, carbon tetrachloride, various chloromatic solvents, variousFreons (believed to be fiuorinated chloroalkanes), aromatic andaliphatic hydrocarbons such as benzene, toluene, gasoline and gasolinefractions, oxygenated solvents such as ethanol, acetone, ethylacetateand other alcohols, ketones, esters, and the like. In all cases, theparticular solvent and solvent vapors should be appropriately selectedto operate empirically with the particular combinations of materials andcompositions employed. Trichloroethylene vapors have been foundparticularly useful for use with photoconductive insulating compositionsof the type described. The developers are tackified almost instantly,whereas the silicone resin of the photoconductive insulating compositionrequires about a minute to soften.

The time necessary to make the powder image tacky or the binder layertacky is dependent on a number of factors such as, for example, thepowder material, the binder layer, Whether heat or vapor is being used,the particular vapor if vapor is being used, temperature applied,whether the vapor contacts the image either directly or through a poroussheet, humidity and other atmospheric conditions, and the like.

The amount of pressure necessary to accomplish transfer, whether it beof the toner image carrying a layer of binder material or whether it beof the remaining binder material, will vary, depending on many factorssuch as the particular binder material, the condition of the tackifiedimage or binder layer, the particular toner material employed, the delaybefore placing the base carrying the softened toner image or softenedbinder layer into a pressure unit, the humidity and temperature of thearea in which the transfer is being carried out, and the like.Generally, it may be stated that pressures in the order of two to thirtypounds per linear inch may be applied.

While this invention has been described in terms of manually performedsteps, and in terms of certain embodiments which have been shown anddescribed, it is to be understood that automatic and semiautomaticdevices as well as other modifications, which will be easily recognizedby those skilled in the art, are intended to be encompassed withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

What is claimed is:

1. The method of forming a stencil for duplicating processes comprisingplacing an electrostatic charge pattern on the photoconductive surfaceof a plate comprising a tackifiable photoconductively pigmentedinsulating binder layer overlying and releasably attached to a supportbase, developing the charge pattern by contacting it with finely dividedelectrostatically charged tackifiable particles, tackifying and pressingthe developed, image between a cover sheet and said plate, separatingthe cover sheet from the plate after the image has fused therebyremoving to the cover sheet the fused image carrying therewith a coatingof the binder insulating layer, tackifying and pressing the remainingbinder material between a porous transfer base and the support base ofthe plate, and stripping the transfer base after the binder material hasfused thereby removing with the transfer base and adhering thereto theremaining binder material.

2. The method of forming a stencil for duplicating processes comprisingsensitizing a xerographic plate comprising a tackifiablephotoconductively pigmented insulating binder layer overlying andreleasably attached to a support base by placing a uniform electrostaticcharge on the photoconductive insulating binder layer, exposing thesensitive xerographic plate to a pattern of activating radiation tothereby form an electrostatic charge pattern, developing theelectrostatic charge pattern by contacting the surface carrying thecharge pattern with finely divided tackifiable particles which areelectrostatically attracted by the electrostatic charges of the chargedpattern, tackifying substantially only the developed image, pressing acover sheet against the tackified developed image, allowing thetackified image to fuse between the binder layer and the cover sheet,separating the cover sheet from the xerographic plate thereby removingto the cover sheet the fused image carrying a coating of the binderinsulating layer of the xerographic plate, softening the remainingbinder layer, pressing a porous transfer base against the remainingbinder layer, allowing the binder layer to harden while the transfersheet remains in contact therewith, and stripping the transfer basethereby removing thereon the remaining binder layer.

3. The method of forming a stencil master for the stencil duplicatingprocess comprising forming an electrostatic charge pattern onthetackifiable photoconductive- 1yv pigmented surface ofa xerographic platecomprising a photoconductive insulating binder layer overlying andreleasably attached to. a support base, developing the charge pattern bycontacting it with finely divided tackifiable electrostatically chargedparticles, tackifying the developed image substantially only andpressing the developed image between a cover sheet and the xerographicplate, separating the cover sheet from the plate after the image hasfused thereby removing to the cover sheet the fused image carrying acoating of the insulating binder layer, tackifying and pressing theremaining binder ma terial between a sheet of porous tissue paper andthe support base of the xerographic plate, and stripping the tissuepaper after the binder material has fused thereby removing with thetissue paper and adhering thereto the remaining binder material.

4. The method of forming a stencil master for the stencil duplicatingprocess comprising sensitizing a xerographic plate comprising aphotoconductive insulating layer of Zinc oxide in a tackifiableinsulating resin binder overlying and releasably attached to a papersupport base by placing a uniform electrostatic charge on thephotoconductive insulating binder layer, exposing the sensitivexerographic plate to a pattern of activating radiation to thereby forman electrostatic charge pattern thereon, developing the electrostaticcharge pattern by contacting the surface of the photoconductiveinsulating layer with finely divided tackifiable electrostaticallycharged particles which deposit due to the electrostatic attractionbetween the charges on the surface of the photoconductive insulatingbinder layer and the charges on the particles, tackifying substantiallyonly the developed image, pressing a cover sheet against the tackifieddeveloped image, allowing the tackified image to fuse while sandwichedbetween the binder layer and the cover sheet, separating the cover sheetfrom the xerographic plate thereby removing to the cover sheet the fusedimage carrying thereon a coating of the binder layer, tackifying theremaining binder material of the plate and pressing a transfer sheet oftissue paper into contact with the remaining binder layer, allowing thebinder layer to harden while the tissue paper remains in contacttherewith, and stripping the tissue sheet from the xerographic plate toremove thereon the remaining binder layer and to thereby form a cutstencil for the stencil duplicating process.

5. The method of forming a silk screen master comprising sensitizing aplate comprising a tackifiable zinc oxide resin binder layer overlyingand releasably attached to a paper support base by placing a uniformelectrostatic charge on the zinc oxide resin binder layer, exposing thesensitive plate to a pattern of light and shadow to be reproduced tothereby form an electrostatic charge pattern thereon, developing theelectrostatic charge pattern by contacting the surface carrying thecharge pattern with finely divided electrostatically charged tackifiableparticles which deposit an image configuration due to the electrostaticattraction between the electrostatic charges on the surf-ace of theplate and the electrostatic charges on the particles, tacifyingsubstantially only the developed image, pressing a cover sheet againstthe tackified developed image, allowing the tacified image to fusebetween the plate and the cover sheet, separating the cover sheet fromthe plate to. thereby remove to the cover sheet the fused image carryingthereon a coating of the zinc oxide resin binder layer, tackifyingtheremaining zinc oxide resin binder layer, pressing a silkscreen againstthe remaining zinc oxide resin binder layer, allowing the layer to fusewhile sandwiched between the silk screen and the paper support base ofthe plate, and separating the silk screen to remove thereon the zincoxide resin binder layer to thereby form a silk screen to be used in thesilk screen duplicating process.

6. The method of forming a stencil master for the stencil duplicatingprocess comprising placing an electrostatic charge patternon thephotoconductive surface of a xerographic plate comprising a tackifiablereleasable photo conductively pigmented" insulating binder layeroverlying a support base, developing the charge pattern by 3 contactingit with finely divided electrostatically charged tacifiable particles,tackifying substantially only the developed image and pressing thedeveloped image between the plate and a cover sheet having adhesivebonding characteristics toward the tacky image, separating the cover 1sheet from the plate after the image has fused thereby removing to thecover sheet the fused image carrying a coating of the binder insulatinglayer, tackifying and pressing the remaining releasable binder materialbetween the support base of the plate and a sheet of porous tissue paperhaw'ng adhesive bonding characteristics toward the remaining bindermaterial, and stripping the tissue paper after the binder material hasfused thereby removing with the tissue paper and adhering thereto theremaining binder material.

7. The method of forming a stencil for duplicating processes comprisingplacing an electrostatic charge pattern on a xerographic plate, saidplate comprising a photoconductive insulating layer on a support basewherein the photoconductive insulating layer includes a fusiblereleasable film forming binder, developing the charge pattern bycontacting it with finely divided electrostatically charged tackifiableparticles, tackifying substantially only the developed image andpressing the developed image between a cover sheet to which the tackyimage is attracted and the plate, separating the cover sheet from theplate after the image has fused thereby removing to the cover sheet thefused image carrying a coating of the binder insulating layer,tackifying and pressing the remaining binder layer between a poroustransfer base to which the releasable remaining binder material isattracted and the support base of the plate, and stripping the transferbase after the binder material has fused thereby removing with thetransfer base and adhering thereto the remaining binder material.

References Cited in the file of this patent UNITED STATES PATENTSGestetner Nov. 9, 1926 Carlson Oct. 6, 1942 UNITED STATES PATENT OFFICECERTIFICATION OF CORRECTION Patent No, 2,949,848 August 23 1960 GeorgeR6 Mott v It is hereby certified that error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

Column 8, line 53 for "an" read in 1 line 56, for "taoiiying" readtackifying line 58 for F'tacified" read tackified column 9, line 2, for"tacifiable" read tackifiable Signed and sealed this 27th day of June1961...

(SEAL) r i Attest: L

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

